Web servers run the Internet, so I would say that they "run everything". Whatever, the question was about whether or not Linux is mainstream. It doesn't really matter if it's highly customized or not. That is actually a selling point of Linux, that you can customize it. How is Stallman keeping Linux from mainstream desktop? He doesn't run anything (Canonical or RedHat or Suse), he is not a developer, he is an activist. And without him there would be no Linux, because there would be no gcc or all the other GNU tools, and no GPL, the license that made Linux successful.
I used now a lot of laptops with Linux and usually it runs everything out of the box. 10 years ego I had problems with a DSL modem, but there was also a driver available. Linux have usually problems with printers and scanners if those vendors chose not to support Linux.